Recently, with the rapid widespread of portable and cordless electronic devices, as driving power sources for such devices, small, lightweight and high energy density secondary batteries have been increasingly demanded. Furthermore, technology development has been accelerated in not only secondary batteries used for small consumer goods but also large secondary batteries for electric power storages and electric vehicles, which require long-time durability and safety. In addition, much attention has been paid to fuel cells enabling long-time continuous use with fuel supplied, rather than secondary batteries that need charging.
A fuel cell includes a fuel cell stack including a cell stack, a fuel supplying section for supplying fuel to the cell stack, and an oxidizing agent supplying section for supplying an oxidizing agent. The cell stack is formed by laminating a membrane electrode assembly that includes an anode electrode, a cathode electrode, and an electrolyte membrane interposed between the anode and cathode electrodes, and a separator onto each other, and disposing an endplate on each of the both end sides in the laminating direction. In the cell stack, it is necessary to laminate the anode electrode, the cathode electrode and the electrolyte membrane onto each other tightly, which is not only for allowing an electrochemical reaction to be carried out uniformly. The end plate and the separator are provided with groove for running the fuel and oxygen (air) as the oxidizing agent therein. Therefore, the anode electrode, the cathode electrode and the electrolyte membrane are laminated tightly in order to prevent fuel or oxygen from leaking out from a portion between the end plate or the separator and the anode electrode or the cathode electrode. In general, a cell stack is fastened as follows. Backing plates whose contact surface to the cell stack is larger than the cell stack are overlapped onto the both end sides of the laminated stack. Then, the entire periphery of protrusion of both backing plates is tightened by a plurality of pairs of a bolt and a nut (see, for example, Patent Document 1).
However, when the backing plates are tightened with bolts and nuts in this way, the fuel cell stack becomes larger with respect to the cell stack by a portion for assembling the bolts and nuts. Therefore, an occupied volume is increased when the fuel cell stack is used in small electronic devices. Furthermore, since backing plates are tightened with bolts and nuts outside the cell stack, the backing plates are warped, so that the fastening force in the center portion of the cell stack is reduced. When a thickness of the end plate is increased in order to prevent this, the fuel cell stack is further increased in size.    Patent Document 1: Japanese Patent Unexamined Publication No. 2006-294366